Program-controlling system



March 10,1931. d 1.5mm 1,795,753

` PROGRAM COIQ'TROLLING SYSTEM l Filed Nov] :5, 192s 2 sheets-sheet 1 Terrfe'Mru/s .056. FAM?.

2.6; ATTORNEY.

N. E. BONN 1,795,753 A' f PRoGRm CONTROLLING sJrsTFllv Y Y vFiled Nov. s, 1925 l alsheat-sneet 2 L ATTORNEY TINE i effecting, in accordance Patented 10, 1931 f UNITED STATES PATENT ori-Ica lN() :l 1 E. BONN, OF PHILADELPHIA,

PENNSYLVANIA, ASSIGNOR TO LEEDS &

PENNSYLVANIA rnoGmcoN'rnoLLme SYSTEM Application med November 3, 1926. Serial No. 145,998.

My inventionrelates to a method of .and apparatus for maintaining a predetermined magnitude of a condition, as thermal, or varyingthe magnitude of such condition by with a predetermined program, application of an agent, as heat, of a character to change the magnitude of the condition involved.

- In accordance with my invention, the mag- A nitude of an efect is varied in accordance with the magnitude` of the condition to be controlled, and 'simultaneously another effect is varied in accordance with a selected program, both effects coacting eonjointly to control the application of the agent, and more particularly, said other effect is the electro-motive-orce across a resistance whose magnitude per unit of time differs for diier ent periods and stillmore particularly said resistance comprises a conductor having suitable resistance elements connected in shunt relation for developi 'g an electro-motiveforce varying in accordance with the desred program.

Further in accordance with my invention, there is provided the form of a closed loop across which is suitably and preferably adjustablyv connected a battery or other suitable source of energy,

and more particularly, the aforesaid loop is slowly rotated with respect to a coacting fixed contact forming a terminal of the circuit influenced by the medium under control.

My invention resides in the method,papparatus and system of the character hereinafter described and claimed,`

For an illustration of some of the forms my apparatus may take, reference is to be had to the accompanying drawings, in which:

Fig. 1 is a diagrammatic view of a system utilizable for substantially uniformly raising the temperature of a heating chamber.

Fig. 2 is a perspective view of an impedance constructed in accordance with my invention.

Fig. 3 is a curve showing a program of temperature changes.

Fig. 4: is a diagrammatic view of another form of my invention.

Fig. 5 is a diagrammatic view o another modified form of my invention,

a vresistance conductor in Fig. 6' is a perspective view of a structure utilizable in connection with the form of my invention illustrated in Fig. 5.

Fig. 7 is acurve showing another program of temperature changes.

F 8 is a diagrammatic view of a form of my invention utilizable with a Wheatstone bridge.

F or' purposes of illustration and without limitation` of my invention, the condition to be controlled is herein illustrated as thermal in character. Accordingly, in Fig. 1, at A there is'shown a chamber, enclosure, furnace, or the like, of suitable size, which may be heated by combustion of any suitable type of fuel, either solid, liquid or gaseous. In the example shown, however, and preferably, chamber A is electrically heated and, therefore, may comprise the shell 1 of sheet metal or equivalent, within which is disposed the hollow tubular heating or resistor element 2, of ceramic or the like, resting upon the bottom member 3 and closed at its upper end by the cover 4.-. Surrounding the member 2 with- 1n the shell 1 is a filling 5 of suitable mineral matter or other material, preferably of poor heat conductivity. Disposed within the wall of member 2 is the helically disposed resistance wire 6 traversed by current which causes the evolution of heat for heating urposes.

As one example of a ield in w ich my invention finds application, chamber A may be assumed as having 4relatively large dimensions and containing a number of automobile bodies whose freshly coated or painted surfaces should be subjected to heat treatment in accordance with some predetermined program. To this end, in the form of my invention illustrated in Fig. ll, the amount of current traversing the resistance wire 6 should be so controlled or regulated as to ensure the the magnitude of the current through resistance wire 6.

1n Fig. 1 B representsa disk of wood or other suitable material keyed to a shaft. 7 rotated at' suitable slow rate by the speed reduc-in gears 8 and 9, the latter being keyed to the iatt 16 driven by a clock or other governed motor 11. Upon the periphery or one face of disk E is suitably secured the resistance conductor C Whose terminals C1 and C2 are connected, respectively, to the conductive rings 12 and 13 rotatable with but insulated fr n the shaft 7 by the insulating mem- Coacting, res ectively, with the d 13 are the Xed brush members 1ich are respectively connected tofs 16 and 17 of the potentiometer` ing the adjustable resistance D ery or other suitable source of to the temperature of the chamable device F, herein shown as ple comprising the Wires 18 and r metals. Connected to Wire ttor 20 leading to a fixed contact coacting with the resistance C.

Wire 19 is a conductor 22 leadinal of the coil of a galvanomecoil terminal being connected hy a conductor: 23 to the conductor 16.

The aforesaid galvanometer coil when travby current actuates lor delects an ectri-caliy conductive pivoted pointer' or needle 24 'to which is connected a conductor leadin to one terminal of a battery or other sui gable source of current H om Whose other terminal leads a conductor 26 Which branches as indicated at 26a and 2Gb, the branched ends bein connected, respectively, to terminals o the electromagnets or windings 27 and 28, Whose other terminals are connected, respectively, by the conductors 29 andl 30 to the respective fixed contacts 31 and 32 disposed closely adjacent the pointer 24 and on opposite sides thereof.

Pivoted between thevwindings 27 and 28 is an armature 33 connected by a conductor 34 to one terminal of a suitable. source of current supply, notl shown, from Whose other terminal leads aconductor 35 connected toone end of the resistance wire 6. Extending from the other end of resistance Wire 6 is a conductor 36, one branched end 36a of which is' posed on one side of armature 33 While the ductor 36a.

. `nieuwe Fig. 1. With disk B so positioned that brush 21 is at the end C1 of resistance C, rotation of said disk may be initiated, as aforesaid, and after an interval of time, the disk and conductor C vvill have rotated to such position that brush 21 contacts with some point Cw on said conductor. At thisv time, it may be assumed that the temperature of chamber A and, therefore7 of thermo couple F is insuiciently high to generate anelectro-)motiver` highv rate.

The pointer 24 of galvanometer G remains in the aforesaid deflected position in enl agement with Contact 32 until some point' 'y of 85 evolve heat Within chamber A at a relatively resistance conductor C comes into" (iontact with brush 21, at which time, due to the relatively rapid rate at Which heat is now being supplied to chamber A, the electro-motiveforce of thermo-couple F has risen suiciently to balance the IR drop across the section C1, Cy of Wire C, whereupon needle 24 resumes its neutral position, thereby opening the circuit through Winding 28, which releases armature 33 and -permits the same to ,.100 assume 1ts neutral posltlon to open the c1rcuit through resistance conductor 6. In ordinary practice, however, the aforesaid balanced condition obtains only momentarily,-

and, hence, instead ofremaining inthe neutral position just described, pointer 24 moves into engagement with contact 31, thereby closing a circuit through winding 27 which, upon energization, attracts armature 33 and at contact 38 completes a circuit through re sistance Wire 6 by Way of resistance 39.

Accordingly, current is supplied to said Wire 6 at a reduced rate,`and heat is evolved Within chamber A at a slower rate than when armature 33 was in engagement with Contact 37. Eventually, under these conditions, as

rotation of disk B and resistance C continues, the IR drop across the active section of said resistance overbalances the electro-motiveforce developed by thermo-couple F, whereupon current is passed lthrough the coil of galvanometer `Gr in such direction as to again deiect pointer 24;4 toward the right, and armature 33 transfers the circuit through resistance Wire 6 from resistance 39 to con- From theforegoing, it becomes apparent that the rate of temperature rise within chamber-A fora given value of current depends solely upon the resistance per unit length Y. chamber.

` 'with time in any desired manner by suita uniform resistance).

of such wire is uniform throughout its length,

the rate of temperatue rise will be substantially uniform, and any non-uniformity in the distribution of resistance therealong results in a corresponding non-uniformity in the rate of temperature rise withinthe heating In accordance with perature within chamber' A may be-changd y distributing the resistance ofthe wire C over or along its length. Tothis end, the resistance wire may be berof sections, 'each wound with wire of a size different from that employed for the other sections. The construction of a composite resistance wire of this character is somewhat diicult, and, therefore, it is desirable that the resistance wire be constructed from wire having a uniform size and that sections thereof be shunted by units of known resistance.

A construction of ,the character last noted is illustrated in Fig. 2, wherein the resistance conductor C has a section c, c1 shunted by the resistance I and another section c2, c3 shunted by the resistance I1. With this arrangement, the temperature of the heating chamber will rise at a substantially uniform rate during the integral of time that elapses while` disk B rotatesfrom the position where contact 21 coacts with the end C1 of said wire until said contact is positioned in contacting relation with conductor C at thepoint c. During the time that disk B rotates from thev lastnoted position until contact 21 coacts with the point c1 of resistance conductor C, the temperature of the heating chamber continues to rise the wire from which shunt I is wound is of However, due to the lower effective resistance per unit length' of section c, c1, as imposed by the shunt resistance I, the rate last mentioned at which the chamber temperature rises, lwill be lower than the rate first mentioned. v v

During the time that the disk B rotates from the position where contact 21 coacts with point c1 until said contact coacts with the end C2 of wire C, the temperature of the heating lchamber rises at one rate, as determined by the resistance wire section c1, c2, at another and different rate as determined by the section c2, c3, andagain at the normal rate as determined by the section c3, C2.

For uniform speed of rotation of disk B, the duration of the various periods during which the temperature in the heating chamber rises, the rates of such temperature rise, and the times when the various periods are initiatcdand terminated may be effected as `desired by suitably selecting` the resistances of conductor C and shunts I and Il, and connecting the latter to conductor C in the my vetion, the am-- formed by utilizing a numat a substantially uniform rate (if `the beginning of the second,

proper regions.` Obviously, any desired number of shunts having desired resistances may be utilized and the shunts may be distributed along conductor C as desired.

In the -form of my invention describe above, the control is such that the temperature of the heating chamber is always rising, and, therefore, at the end of the operation maximum value. Under some circumstances, it is desirable that the temperature of the heating chamber be raised to a certain value, and that thereafter a cooling period shall ensue. Moreover, it may be desirable, during certain intervals of time, to maintain the temperature of the heating chamber sub.- stantially constant.

'In accordancewith the last-named phase of my invention, I have diagrammatically illustrated in Fig. 4 a. control the conductors 26, 29 and 30 may be assumed, in a manner similar to that described above,

- as controlling the application of heating current to the heating chamber, not shown, but with respect-to the temperature of which the thermo-couple F is responsive. For purposes of explanation, the conductor C, of uniform resistance throughout, may be assumed as mounted on a disk similar to the disk B of Fig. 1, which is slowly rotated in any suitable manner past the xed contact 21 engaging the said conductor C. Connected to the ends C1 and C2 of resistance wire C is the conductor 41, to which is connected a conductor 42 including the fixed resistance J, the battery or other suitable source of current K and the adjustable resistance L.- Conductor 42 is extended into conductive engagement system whereinthe heating chamber temperature 1s at its sie 'miv

with resistance wire C in the manner hereinafter described.

In Fig. 3, there is illustrated a curve showing a program or chart of temperature changes or conditions' over a twenty-four hour period. Should it be desired to control the temperature of aheating chamber in accordance with this program, the resistance conductor C o f Fig. 4 and its supporting disk B should be so arranged as to rotate continuously and uniformly once and only once during a twenty-four hour period. According to the curve, there are six intervals duri which the temperature either cha 4 es in va ue or is maintained constant. nsequently, resistance conductor C should be divided into six sections, and if six inches in length, would advance one-'quarter inch during each hour. Therefore, in order to vary the temperature of the heatin chamberfin accordance with the program, c an es in the amount of heat evolved must be e ected at sixth, twelfth, sixteenth and nineteenth hour from the beginning of the cycle. 'Io this end, conductive taps 43, 44, 45, 46 and 47 are conductively secured to resistance wire C at distances, re-

spectively, of 0.5, 1.5, 3.0, 4.0 and 4.75 inches from its end C1. Assuming that the resistance conductor C is 30|,ohms, that the potentiometer current is 10 milliamperes, and that p 30 microvolts is the uniform increment per degreein the thermal electro-motive-force of thermo-couple F, the resistances of the various' shunts may be tabulated as follows:

2.31 ohms resistance, which is connected to conductors 41 and 43. The section 43-44 is tied together or bridged by the short-circuit-v ing bar or rod M1 connected to conductors 43 and 44, and the sections 4445 and 45-46 are bridged, respectively, by coils M2 and M3, respectively, having resistances of 2.37 and 3.62 ohms, and connected, respectively, to the conductors 44 and 45 (the latter being connected to conductor 42 of the potentiometer circuit) and 45 and 46. The section 46-47 is tied together or bridged by the short-circuiting bar M4 connected to conductors 46 and 47 and section 47-02 is bridged b the coil M5 having a resistance of 1.05 ohms and connected to the conductors 47 and 41. f

During the rst two hours ofoperation,

while conductor C rotates from the position' where contact 21 coacts with the end C1 of `conductor C until said contact engages the int connected to tap-01T conductor 43, the I drop, as determined by coil M, to be balanced a ainst the, electro-motive-force developed ythermo-couple F is increasing, and, hence, the temperature of the heatin chamber rises, as designated by section m ot the cuve of Fig. 3. During the next four hours, conductor C rotates from the position where contact 21 engages tap-off conductor 43 to such position that said Contact engages the point of c onductor C connected to tap-off conductor 44. During this riod, due to the presence of the vbar M1, t ere is no further increase in theIR drop of conductor C, and,.hence, the temperature ofthe heating chamber remains constant as indicated by section mi of the curve of Fig. 3. During the next six hours, conductor C rotates from the position where contact 21 engages tap-olf conductor 44 to the position where contact 21 engages conductor 45. During this period,

the IR drop, as determined by coil M2, tobe balanced against the electro-motive-force developed by thermo-couple F isgagain increasing, and, therefore, the temperature of the heating chamber rises, as designated by section m2 of the curve of Fig. 3. v

V Since tap-od' conductor 45 is connected to conductor 42, which is one terminal of the potentiometer battery K whose other is conductor 41 connected to the end Cl of resistance conductor C, the maximum IR drop to be balanced by the electro-motive-orce of thermo-couple F is developed when contact l21 coacts with the portion of conductor C to which tap-off conductor 45 is connected. At this time, the temperature of the heating chamber has reached its highest value, and thereafter the temperature must remain constant'or decrease in .value As indicated in Fig. 3, during the next two hours of operation the temperature of the heating chamber falls somewhat rapidly, since the rate of the IR drop, as determined by coil M3, to be balanced against the electro-motive-orce developed by thermo-couple F is decreasing somewhat rapidly. Accordingly, the temperature of the heating chamber falls, as designated by section lm3 of the curve of Fig. 3.1 During the next three hours,'while resistance conductor C rotates from the position where contact 21 engages tap-oli' conductor 46 to such position that said Contact engages tap-olf conductor 47, the IR drop, to balance against the electro-motive-force developed by thermocouple F, remains constant due to the preslence of the barM4. During this period, the temperature of the heating chamber remains constant, as designated by lthe section m4 of the curve of Fig. 3. During the next tive hours, resistance conductor C rotates from the position Where contact 21 enga-ges tap-off conductor'47 to such position that said contact engages the end C2 of said resistance conductor. During this period, the rate of the IR drop, as determined by coil M5, to be balanced against the electro-motive-force developed by thermo-couple F, is again decreasing, and hence the temperature of the g heating chamber falls, as designated by section m5 of the curve of Fig. 3.

It will be observed that one terminal of the potentiometer battery K is connected by conductor 41 to both ends C1 and C2 of the resistance conductor C. It results, therefore, that said terminals of resistance wire C are at the same potential, and, therefore, with this form of invention, the ends C1 and C2 may be mechanically connected together, whereby resistance conductor C forms a closed circle' or loop. Accordingly, the program ma be repeated as vmany tlmes as desirable wit out stoppinto turn the resistance conductor by hand. his vfeature is of particular importance in certain industrial processes where n certain sequence or program should be repeated continuously. l

In the example shown, the terminal of the potentiometer battery K, towhich the con- Vductor 42 is connected, is shown `as permanently connected to resistance conductor C midway of its ends, and it is due to this feature, together with the uniform speed of rotation of the resistance conductor C, that the highest temperature in the heating chamber was reached at t-he time 'the program was onelialf completed. Obviously, however, said terminal 42 may be connected nearer either eiid of resistance conductor C, as found desirable, thereby causing the temperature of the heating chamber to reach maximum value either before or after the program is one-half completed. To this end, it may be desirable to provide an adjustable connection between conductor 42 and the resistance conductor C.

In Fig. 4 there is supplementarily illustrated a well-known arrangement for determining the correct strength of current through the potentiometer resistance C from the source K. As herein shown, conductor 22, which is connected from one wire of thermo-couple F to one terminal of the galvanometer coil G, has interposed therein the movlable switch element 48 and adjustable contact 49. A second contact element 50, likewise co-actable vwithl switch element 48, is connected by a conductor 51 to one terminal of a standard cell S. C., whose other terminal is connected by a conductor 52 to one`ter minal of the potentiometer battery'K. To determine correct strength of the current through resistance wire C from the source of current K, the 'resistance L is adjusted to such value that when the movable switch element 48 is in engagement with contact 50, the coil of galvanometer G will not deflect, indicatj the fall of potential through the resistance J due to the current from the source K is equal and opposite to the electro-motiveforce of the standard cell S. C.

in the forms of my invention heretofore ing that described, the resistance conductor has been described as shunted with various resista-noos permanently connected in circuit and capable of performing a single definite program.

Such an arrangement is suitable for many industrial applications, but is insuliiciently flexible for others, inasmuch as more than one program may not readily be performed with a single instrument. To meet a condition of the character last noted, I have illustrated in- Figs. 5 and 6 a form of my invention having provision for readily modifying the shunt characteristics of the resistance wire in such manner that any desired type of program may be eifected.

As particularly illustrated in Fig. 6, there is secured to the shaft 7 driven at uniform slow speed in a clockwise direction the conductive rings 53, 54, 55, 56, 57, 58 and 59, insulated from each other and from the'hshaft'7`by the insulating member 14a. Likewise disposed on vthe shaft 7 is a disk B, which, as described above, may carry on its periphery or on oneface the resistance conductor C. i Conductors 61, 62, 63, 64, 65, 66 and 67, connected to and equidistantly spaced along resistance conductor C, extend and are respectively vconnected to the conductive rings 53, 54, 55, 57,

' 58 and 59. Contactingrespectively with the aforesaid conductive rings are individual brush elements to which are respectivel connected the conductors 68, 69, 70, 71, 2, 78 and 74, terminating, respectively, in binding posts or other terminals 7 5, 76, 77, 78, 79, 80

and 81, Fig. 5, located on a suitable panel,

not shown, or elsewhere, as desirable.

Branching from terminal 81 is a conductor 82 connected to one terminalof an adjustable resistance N, to whose other terminal is con nected a conductor 83 connected to one ter= -minal of the fixed resistance O, whose other terminal is connected by conductor 84 to oneA I' terminal of another fixed resistance P, whose meter cell or other source R, whose other ter minal is connected to' a conductor 88 terminating in the contact 89, which may be placed in conductive en agement with any of the binding posts 75, 6, 77, etc. In the form of my invention illustrated in Fig. 5, the condiic tor 23 leading fromv one terminal vof the coil .of galvanometer G is in effect connected to the end C1 of resistance conductor C, since it leads to the terminal 75, which is connect ed to said end of conductor C through conn ductor 68, its theretobonnected brush, conductivering 53 and conductor 61.

Interposed in the conductor 22 leading from thermo-couple F is the fixed contact 90 and movable switch element 91. A second fixed contact 92, likewise co-actable with the movable contact 91, is connected by a con ductor 93 to one terminal of the standard cell S. C. whose other terminal is connected by the conductor 94 to the conductor 84 between the fixed resistances O and P. Branching from the conductor 83 between the adjustable and fixed resistances N and O is a conductor 95 connected to conductor 23 and having a. switch element 96 interposed therein. Branching from conductor 85 between the adjustable and fixed resistances Q, and P is the conductor 97, likewise connected to conductor 23 and havlilng the switch element'98 in circuit there= wit It may be assumed, for purposes of illus-V tration, that the resistance conductor C of Figs. 5 and 6 has a length of six inches, a resistance of nine'ohms and the rotative speed thereof is one revolution in six hours. It ma also be assumed that resistance conductor has been divided into six equal. sections and that the wires 61, 62, 63, etc., form the termigree Fahrenheit of 0.00003 volts and with the sections not shunted, the rate oi temperature change within the heating chamber 1s 500 degrees per hour.

From the` foregoing data, the resistances of shunt coils for changing the temperature within the heating chamber at different rates, such as 400, 300, 100 and 0 degrees per hour, may be tabulated as follows:

Rate- Volts Res.

de re- Cun'ent re Agg Shunt Remarks per quired quired 500 015 01 1. 5 1. 5 none 400 012 01 1. 2 l. 5 6. 0 300 009 01 0. 9 1. 5 2. 25 m0 .006 .0l 0.6 1.5 1.0 100 003 01 0. 3 1. 5 375 0 00B 01 0. 0 1. 5 0 Short circuit If desired, the various resistance coils may be marked in terms of ratesof temperature change, so that-an unskilled operator may readily select a desired program. For example, should it be desired to maintain thetemperature of the heating chamber in correspondence with the curve illustrated in Fig. 7, it will be necessaryel 1. To raise the temperature of the heating chamber from 100 degrees F. to 600 degrees F. in one. hour. l

l.2.. To further raise the temperature to 800 degrees F. in two hours. v

3. To maintain the heating chamber at 800 degrees F. for one hour.

4. To cool the heating chamber to 200 degrees F. in two hours.

During the first hour, or while the resistance conductor C rotates from the ositien where contact 21 co-acts with its end untii said contact co-acts with the point on said resistance conductor to which conductor 62 is connected the rate of temperature rise is 500 degrees' per hour, and since, as stated above, this is the rate of temperature change as imposed by resistance conductor C alone,

no shunt is required between binding posts and 76. During the next two hours, or while the resistance conductor C moves from Athe position where contact 21 co-acts with resistance conductor C immediately adjacent conductor 62 to the point where said contact co-acts with the ortion of said resistance conductor immedlately adjacent contact 64, the rate of temperature rise is to be 100 degreesdper hour. Accordingly, a coil marked 100 egrees per hour should -be connected between binding posts 76 and 77, and another similar coil should be connected between binding posts 77 and 78. During thefourth hour, or while resistance conducter C is movweaves ing from the position where contact 21 coacts therewith immediately adjacent conductor 64 until said contact cont-ts with the resistance conductor immediately adjacent contact 6,5, no chan e in temperature is to take place, and, there ore, bindin po-y 1.a 78 and 79 should be short-circuited. airing the iifth and sixth hours, or while resista` .se conductor` C is moving from the position wherecontact 21 co-acts therewith immediately adjacent conductor 65 to a position where said contact co-acts, with the ends C2 of said resistance conductor, the rate of temperature change shall be 300 degrees F. per hour, and, therefore, a' coil marked 300 degrees per hour should be connected between hindi posts 79 and 80, anda similar coil should be connected between binding posts 80 and 81.

According to the curve of Fig. 7, the temperature of the heating chamber shall start decreasing with the beginning of the fifth hour, and, therefore, the movable terminal 89 of the potentiometer battery R is conductively related to the binding post or terminal 79. The two branches of the potentiometer circuit are then separately adjusted by moving switch element 91 from engagement with contact and placing it into engagement with contact 92. Thereafter, switches 96 and 98 are closed in succession and resistances N L. 1

ing chamber may be initiated as desired by conductively relatinthe movable contact 80' of the potentiometer attery with any desired binding post or terminal 76 to 8i?, inclusive.'

However, each new position te which the aforesaid Contact 89 is moved necessitates adjustment of the resistance of the potentiometer branches as indicated above.

in Fig. 8, there is illustrated a modified form of my invention wherein a balancing action is effected by utilizing a `Wheatstone bridge. As shown, a device S, as a resistance thermometer, responsive to the temperature of chamber A and whose resistance, in the example shown, increases proportionately with its rise in temperature, is included by the conductors 100 and 101 in one arm of the bridge, while in a corresponding arm of the `bridge is connected a suitable device whose which branches a conductor102 connected at T to the conductor 100, to which also is connected the conductor 17 leading to the endv C2 ofresistance C. Conduct-or 16, branching from the end C1 of resistance C, may be con- D icc i It will be observed that cooling of the heatuneeted to one terminal of a xed resistance U, whose other terminal is connected at T1 to a conductor 103 leading to one terminal of the coil of galvanometer Gr. In the other arms of the bridge are the resistances U1 and U2, adjacent terminals of which are joined at T2. The otherterminal of resistance U1 is connected to conductor 103 at T1, while the other terminal of resistance U2 is connected at T3 to the conductor 101, from which connection branches a conductor 104 leading to the other terminal of the nometer G. From the respective terminals of a. battery or other source of current V are connected the conductors 105 and 106 connected, respectively, to the points kT and T2.

With the arrangement illustrated in Fig.

v8, when theresistan'ce of the 4bridge arm conl sistance coil 6 to decrease the amount of taining vthe resistance thermometer S 1ncreases in value above that of the correspondthe shuntedA resistance ing arm containing conductor C, the bridge is unbalanced and current flows through the coil of galvanometer G in such direction that its pointer 24 is deflected toward the left, whereby, as described above in connection with Fig. 1` the resistance 39 is included in the circuit of re heat evolved in chamber A. lSimilarly, when the resistance of the bridge arm containing thermometer S decreases in value below that of the corresponding arm containing shunted resistance conductor C, current flows through the galvanometer coil Gr in reverse direction and pointer 24 is moved toward the right to transfer the circuit through the coil 6 from resistance 39 to conductor 36a, thereby increasing the amount of heat evolved in chamber A.

It follows, in view of the foregoing explanation of my invention, that it is fundamentally important that in the heating chamber the ratio of the energy supply to the,

energy` loss be such that with thegalvanometer pointer 24 in engagement with contact 32, the temperature rises at a rate higher than the highest rate demanded by the program, and that with the galvanometer pointer in engagement with contact 31, the heating chamber cools at a faster rate than the quickest rate of cooling required by the program.

It will be seen, therefore', that in the present improved method of temperature-control, wherein the control of temperature con'- ditions is carried on ance with a predeterminedv program, heat is'applied at two different rf tes alternately, one rate providing for heat-application greater than that required to follow exactly the program, the vother rate providing for heat-application less than that required to follow exactly the program. In other words, in the present improved method of temperatureycontrol substantially in accordance with a predetermined program, heat is applied at coil of galvav substantially in accordvductor C may be different rates alternately, any rate providing for heat-application either greater than or lessv than that required to follow exactly the program.

It will be seen trol consistsin producing through the thermo-couple F an `electrical eiect in the potentiometer circuit which varies in magnitude in accordance withthe magnitude of a condition such as the temperature condition in chamber A, in utilizing the resistance C to produce an electrical effect in the potentiometer circuit varying in'magnitude in accordance with a program which is lpredetermined by the resistance per unit length of resistance C, and jointlyutilized the two effects through galvanometer Gr, relay 27 -28 and associated parts to control the magnitude of said condition. I

In the present improved controllsystem, further, the relay 27 -28 and associated parts constitute means oper ble to effect controlthat A, and the resistance ing action ofthe governing' means or gali vanometer G. I

The relay 27-28 and associated parts constitute, in another sense, governing means for the heat-applying means or resistance wire'6, the galvanometer G and associated parts constitute means responsive to conditions of current-unbalance in the potentiometer circuit operable upon occurrence of such conditions to efect'governing action of the governing means or relay 27-28 and associated parts for wire 6.v

Although the foregoing description of my invention relates somewhat specifically to arrangements for heating a chamber electricallv, it shall be understood that the heating chamber may be heated by combustion of suitable fuel, and that the galvanometer o r equivalent may be utilized, for example, control the speed of. a device feeding solid fuel or to open or close a valve in a conduit traversed by liquidA or gaseous fuel.

It shall alsobe understood that in lieu of the arrangement described, the resistance conmaintained in a stationary position and that motion at suitable rate may -be imparted to the contact 21m-acting therewith.

The v term further that in the present improved control system, the method of conf vri such as the temperature associated parts con-v intended to include impedance where the latter term might more properly be applied in systems other than those disclosed but which embody the invention as claimed.

What I claim is:

1. A control system comprising a potentiometer circuit including a conductor in the form of a closed loop, a source of potential connected thereacross, and a contact adjust- 10 able circnmferentially of said loop connected to said source, a circuit connected to said loop includin a contact adjustably co-acting therewit and means for eiecting relative movement between said loop and sald secondnamed contact.

2. A control system comprising a poteny tiometer circuit including resistance in the form or' a closed loop and whose magnitude per unit of timediiers for diierent periods,

a circuit connected to. said loop including a Contact adjustably co-acting therewith, and means for eecting relative movementV between said loop and contact.

3. A' control system comprising a :potentiometer circuit including a resistance in the form of a closed loop and a second resistance bridging a section of said loop, a circuit connected to said loop includin a. contact adjustably engageable with the ridged section $0y and with a section of the resistance loop beyond the bridged section, and means for effecting relative movement between said loop and contact. 4. A control system comprising a potentiometer circuit including a resistance 1n the forni of a closed loop, a second resistance `bridging asecticn of said loo and means for connecting the terminals og) another loop section together, a circuit connected to said v4c loop including a contact adjustably engage-l able with the bridged section and with a section of the resistance loop beyond the bridged section, and means for eecting relative movement between said loop and contact.Y

y A- NRN E. BONN., y 

